A physically active lifestyle is almost certainly beneficial
The amount of glucose in the blood has to be maintained within narrow limits for the proper functioning of the body. And the concentration of glucose in the blood is balanced by the processes that add glucose to the blood in the form of food and drink intake and processes that remove glucose from the blood in the form of uptake of sugar by the nervous system and periphery tissues. Following a meal, blood glucose level increases and must be kept under control by the hormone insulin, which is secreted from the pancreas. Diabetes is a disease whereby the body is unable to regulate the concentration of glucose in the blood and is also impaired in its ability to metabolise carbohydrates. There are therefore two main forms of the disease: insulin-dependent diabetes mellitus (IDDM or type I) and non-insulin-dependent diabetes mellitus (NIDDM or type II).
IDDM or type I diabetes, is a disease that afflicts 5-10% of all cases of diabetes and occurs mainly in young people. In this form of diabetes, the pancreatic beta cells that produce insulin are destroyed and the body is unable to produce sufficient amounts of insulin. People with IDDM require daily injections of insulin for life to help with carbohydrate metabolism and although they can benefit from a well-structured programme of regular exercise, such a programme will not cure or prevent this form of the disease. NIDDM or type II diabetes is the more prevalent form of diabetes and accounts for 90-95% of all cases. In this form of the disease, the body is impaired in its response to insulin (i.e. insulin resistance) and in some cases, there may be insulin insufficiency as well. Type II diabetes is more prevalent in adults aged 40 years and above and is associated with an increase in body weight. Not surprising then, over 80% of people with NDDM are overweight or obese. In Singapore, the prevalence of type II diabetes in the population is 9%, with Indians having the highest proportion (15.8%), followed by Malays (11.3%) and then the Chinese (8.0%).
Diagnosis of NIDDM
A predominant characteristics and one that precedes the disease, however, is insulin resistance or impaired glucose homeostasis. Both impaired glucose homeostasis and type II diabetes are associated with an increased risk of developing atheroscelerosis (narrowing of the blood vessels due to the formation of plaque), hypertension (high blood pressure), heart disease, stroke and other forms of micro-vascular disease like retinopathy and blindness, as well as increased risk of infection. Such conditions severely reduce the quality and expectancy of life. Recent and past research consistently show that the increased prevalence of impaired glucose metabolism and NIDDM go hand-in-hand with the urbanisation of various cultures. For example, improved glucose tolerance in urbanised. Australian aborigines was shown when the subjects returned to their traditional hunter-gatherer lifestyle. Others have reported better glucose tolerance and amelioration of NIDDM in more physically active populations compared to their more sedentary peers. Research data on the efficacy of exercise in the treatment of glucose intolerance is buttressed by a series of studies conducted by Manson and his colleagues in the 1990s. In one of his studies, the risk of developing NIDDM was substantially less in female subjects who were engaged in vigorous exercise once a week, compared to those who exercise less frequently, even after adjusting for differences in Body Mass Index. In another study, he reported that male doctors who exercised vigorously five times a week exhibited a 42% lower risk of developing ade-adjusted NDDM than those who exercised less than once a week.
The results were particularly evident in subjects who were overweight. A number of studies also show that although exercise training brought out improved glucose tolerance, the gains were very quickly lost over just 10 days of inactivity.
Young people in comparison to older people
There is a strong association between aging and the development of insulin resistance, which may explain the increased prevalence of glucose intolerance and NIDDM among the elderly. Even then, the impairment of insulin in older people may not be due to aging per se. It appears that up to 70 years, insulin action is determined more by changes in lifestyle such as increased physical inactivity, a poor diet and an increase in body fat, than by aging. Indeed, older people who are exercise-trained and are leaner have enhanced insulin action, when compared to untrained older people.
Young healthy athletes who maintain a physically active lifestyle typically have a reduced insulin response to a glucose challenge. Similar responses are possible from both aerobically trained as well as strength-trained athletes and the benefits can be harvested with just seven days of training. However, the benefits are also quickly lost with the cessation of training.
Conclusion
The benefits of a physically active lifestyle and exercise training in the prevention and treatment of NIDDM are robustly supported by both current and past research. The adaptations that occur within exercise are quickly lost within 14 days with physical inactivity, emphasising that the physically active lifestyle must be maintained for the protective benefits to be sustained. It appears that exercise programmes that involve large muscle groups such as walking, swimming and weight training are advantageous for the prevention and treatment of insulin resistance in NIDD in both young and old people.
Labels: carbohydrate metabolism, IDDM, impaired glucose homeosatsis, insulin insufficiency, insulin resistance, insulin-dependent diabetes mellitus, NIDDM, non-insulin dependent diabetes mellitus
